x=+-П/6+Пk
Объяснение:
8cos2x=2cos4x+5
8cos2x=2(2cos^22x-1)+5
8cos2x=4cos^2(2x)+3
cos2x=t |t|<=1
8t=4t^2+3
4t^2-8t+3=0
t=(4+-sqrt(16-12))/4
t=(4+-2)/4
t=3/2 t=1/2
cos2x=1/2
